JP6984961B2 - Exhaust gas purification filter - Google Patents

Description

The present invention relates to an exhaust gas purification filter.

Exhaust gas emitted from an internal combustion engine such as a gasoline engine or a diesel engine contains a particulate matter called particulate (hereinafter, may be appropriately referred to as "PM"). In order to collect PM in the exhaust gas and purify the exhaust gas, an exhaust gas purification filter is arranged in the exhaust passage of the internal combustion engine.

As an exhaust gas purification filter of this type, for example, Patent Document 1 describes a diesel particulate filter (hereinafter, may be referred to as “DPF”) that collects PM emitted from a diesel engine. Specifically, in the same document, in order to suppress the increase in pressure loss due to the increase in PM deposition, the partition wall forming a plurality of cells is made of a porous base material having a porosity of 45 to 70%, and is a base material. When the average pore diameter measured by the mercury intrusion method is (A) μm and the average pore diameter measured by the bubble point method is (B) μm, it is represented by {(AB) / B} × 100. A DPF in which the average porosity difference ratio is 35% or less, the average porosity (B) is 15 to 30 μm, and the maximum pore diameter measured by the bubble point method is 150 μm or less is disclosed. ..

Japanese Unexamined Patent Publication No. 2006-95352

The amount of PM emitted from a gasoline engine is overwhelmingly smaller than the amount of PM emitted from a diesel engine. However, since the number of PMs has been restricted, a gasoline particulate filter (hereinafter, "gasoline particulate filter") that can collect PM emitted from a gasoline engine even in a vehicle having a gasoline engine (hereinafter, "gasoline vehicle") is appropriately used. It is sometimes called "GPF").

Regulations on the number of PMs in gasoline-powered vehicles are expected to become stricter year by year. In order to clear future regulations, it is more important to improve the PM collection rate at the initial stage. By the way, in GPF, a catalyst for purifying exhaust gas may be coated. When the catalyst is coated, the pores of the partition wall are partially closed, so that the PM collection rate and the pressure loss (hereinafter, may be appropriately referred to as “pressure loss”) are deteriorated. In addition, since the temperature of the exhaust gas is high and the flow velocity is high in the gasoline engine, the pressure loss tends to increase as compared with the diesel engine. Therefore, it is difficult to improve the PM collection rate and reduce the pressure loss while purifying the exhaust gas with a catalyst in the GPF. Therefore, as a means for clearing future regulations, there is an increasing possibility that a GPF that separates the two functions of collecting PM and purifying exhaust gas with a catalyst and does not coat the catalyst is adopted. However, even if the catalyst is not coated, there is a trade-off relationship between the improvement of the PM collection rate and the reduction of the pressure loss, so that there remains a problem that the pressure loss increases when the PM collection rate is improved.

In addition to the above, PM contains solid carbon (suit) and ash (Ash) derived from engine oil and the like. Ash is a component that remains even after the PM regeneration process. In gasoline-powered vehicles, it is important to suppress the increase in pressure loss due to the residual ash accumulated over time. Although the residual ash accumulates in the DPF over time and the pressure loss increases, the exhaust gas temperature is low and the exhaust layout has a margin, so suppressing the increase in pressure loss after ash accumulation has not been a problem so far. ..

The present invention has been made in view of the above problems, and an exhaust gas purification filter capable of ensuring an initial PM collection rate, reducing an initial pressure loss, and suppressing an increase in pressure loss after ash accumulation will be provided. Is to be.

One aspect of the present invention is an exhaust gas purification filter (1) arranged in an exhaust passage of a gasoline engine.
A partition wall (11) having a large number of pores (110) and
A plurality of cells (12,121,122) partitioned by the partition wall, and
It has a sealing portion (13) that alternately seals a plurality of the above cells at both ends of the filter.
When the average pore diameter of the partition wall is A μm and the average surface opening diameter of the pores on the partition wall surface is B μm.
A ≧ B is satisfied, and A is 5 μm or more and less than 15 μm.
Ri der percentage 30% or less calculated by the 100 × formula (A-B) / B,
In a state where ash (23) of 20 g / L or more and 40 g / L or less is deposited,
The gas permeability coefficient of the partition wall at _{a position (X 10} ) 10 mm from the filter end face (15) on the exhaust gas inflow side _{is k 10} , and the center between the filter end face on the exhaust gas inflow side and the filter end face (16) on the exhaust gas outflow side. When the gas permeability coefficient of the partition wall at the position (X _{C ) is k c} ,
The exhaust gas purification filter (1) has a gas permeability coefficient ratio of k _c / k ₁₀ of 1.5 or less.

The exhaust gas purification filter has the above-mentioned specific configuration, and in particular, when the average pore diameter of the partition wall is A μm and the average surface opening diameter of the pores on the partition wall surface is B μm, A ≧ B is satisfied and the value of A is satisfied. , And the ratio calculated by the formula of 100 × (AB) / B is set to a specific range. Therefore, according to the exhaust gas purification filter, it is possible to secure the initial PM collection rate, reduce the initial pressure loss, and suppress the increase in pressure loss after ash accumulation.

The reference numerals in parentheses described in the scope of claims and the means for solving the problem indicate the correspondence with the specific means described in the embodiments described later, and limit the technical scope of the present invention. It's not a thing.

FIG. 1 is a perspective view of an exhaust gas purification filter according to the first embodiment. FIG. 2 is a cross-sectional view taken along the filter axis direction of the exhaust gas purification filter according to the first embodiment. FIG. 3 is a diagram showing the flow of exhaust gas in the exhaust gas purification filter according to the first embodiment. FIG. 4 is a diagram showing an example of a reflected electron image of the partition wall surface obtained by a scanning electron microscope obtained when measuring the surface opening diameter of pores on the partition wall surface in the exhaust gas purification filter according to the first embodiment. .. FIG. 5 is a diagram showing an example of a binarized image obtained by binarizing the reflected electron image of FIG. 4. FIG. 6 is a diagram schematically showing the microstructure of PM. FIG. 7 is an enlarged cross-sectional view of the partition wall on which the surface side of the partition wall into which the exhaust gas flows is shown. FIG. 8 is a diagram showing how PM is segregated in the vicinity of the surface opening in the partition wall shown in FIG. 7. FIG. 9 is a diagram showing how the ash contained in the PM remains after the PM shown in FIG. 8 is regenerated. FIG. 10 is a diagram showing how PM is collected again in the state where the residual ash content shown in FIG. 9 is present. FIG. 11 is a diagram showing a state in which ash crosslinks the surface openings of pores on the partition wall surface by further repeating PM deposition and PM regeneration processing from the state of FIG. 10. FIG. 12 is a diagram showing how the ash that crosslinks the surface opening shown in FIG. 11 is peeled off by the flow of the exhaust gas, and the peeled ash is transported to the sealing portion on the gas outflow side. FIG. 13 is a diagram showing a method of measuring the gas permeability coefficient of the exhaust gas purification filter. FIG. 14 (a) is a diagram showing an example of a tape for forming a sealing portion attached to the upstream end face of the measurement sample collected from the exhaust gas purification filter, and FIG. 14 (b) is a diagram showing an example of the tape for forming a sealing portion, and FIG. 14 (b) is from the exhaust gas purification filter. It is a figure which showed an example of the tape for forming a sealing part attached to the downstream end face of the collected measurement sample. FIG. 15 is a diagram showing an example of a relationship diagram between a gas flow velocity (X-axis) and a pressure loss (Y-axis). FIG. 16 is a diagram showing the relationship between the gas permeability coefficient ratio k _c / k _{10 and the pressure drop increase rate obtained in the experimental example.}

(Embodiment 1)
The exhaust gas purification filter according to the first embodiment will be described with reference to FIGS. 1 to 15. As illustrated in FIGS. 1 to 3, the exhaust gas purification filter 1 of the present embodiment is arranged and used in an exhaust passage (not shown) of a gasoline engine. That is, the exhaust gas purification filter 1 is a gasoline particulate filter (GPF) capable of collecting PM2 (see FIG. 6 described later) discharged from the gasoline engine. The direction of the arrows on both ends shown in FIGS. 1 to 3 is defined as the filter axial direction X of the exhaust gas purification filter 1.

The exhaust gas purification filter 1 has a partition wall 11, a plurality of cells 12, and a sealing portion 13. As illustrated in FIGS. 1 and 2, the partition wall 11 has, for example, a grid-like shape in a cross-sectional view perpendicular to the filter axial direction X inside the skin portion 14 formed in a cylindrical shape such as a cylinder. Can be provided to exhibit. In the exhaust gas purification filter 1, the partition wall 11 and the skin portion 14 can be formed of, for example, cordierite or the like. Further, the sealing portion 13 can be formed of, for example, ceramics such as cordierite, but may be made of other materials.

The plurality of cells 12 are partitioned and formed by the partition wall 11. The cell 12 is surrounded by the partition wall 11 and forms a gas flow path. The expansion direction of the cell 12 usually coincides with the filter axis direction X. In the cross-sectional view perpendicular to the filter axis direction X, the cell shape can be a quadrangular shape, for example, as illustrated in FIG. The cell shape is not limited to this, and may be, for example, a polygonal shape such as a triangular shape or a hexagonal shape, or a circular shape. Further, the cell shape may be composed of a combination of two or more different shapes.

As illustrated in FIG. 2, the plurality of cells 12 are alternately sealed by sealing portions 13 at both ends of the filter. Specifically, the plurality of cells 12 are first opened to the filter end face 15 (upstream side end face) on the exhaust gas inflow side and closed by the sealing portion 13 at the filter end face 16 (downstream side end face) on the exhaust gas outflow side. It can have a cell 121 and a second cell 122 that is open to the filter end face 16 on the exhaust gas outflow side and is closed by the sealing portion 13 at the filter end face 15 on the exhaust gas inflow side. As a result, as illustrated in FIG. 3, the exhaust gas G flowing into the first cell 121 from the filter end surface 15 on the exhaust gas inflow side flows in the first cell 121 and also in the porous partition wall 11. It reaches 2 cells 122. The exhaust gas G that has reached the second cell 122 flows in the second cell 122 and is discharged from the filter end surface 16 on the exhaust gas outflow side.

The first cell 121 and the second cell 122 are alternately arranged so as to be adjacent to each other, for example, in the horizontal direction orthogonal to the filter axial direction X and in the vertical direction orthogonal to both the filter axial direction X and the horizontal direction. Can be formed side by side. In this case, when the filter end surface 15 on the exhaust gas inflow side or the filter end surface 16 on the exhaust gas outflow side is viewed from the filter axial direction X, the first cell 121 and the second cell 122 are arranged in a check pattern, for example. The first cell 121 and the second cell 122 adjacent to each other are separated by a partition wall 11 in between.

The partition wall 11 has a large number of pores 110, as illustrated in FIG. Specifically, the pore 110 in the partition wall 11 includes a communication hole 111 that communicates between the first cell 121 and the second cell 122 that are adjacent to each other. The pore 110 in the partition wall 11 may include a non-communication hole 112 that does not communicate between the first cell 121 and the second cell 122 that are adjacent to each other, in addition to the communication hole 111.

In the exhaust gas purification filter 1, when the average pore diameter of the partition wall 11 (that is, the average pore diameter inside the partition wall 11) is A μm, the average pore diameter A is in the range of 5 μm or more and less than 15 μm.

The average pore diameter A of the partition wall 11 is measured by a mercury porosimeter using the principle of the mercury intrusion method. Specifically, a test piece is cut out from the exhaust gas purification filter 1. However, the portion where the sealing portion 13 is present is excluded. The test piece is a rectangular parallelepiped having dimensions in the direction orthogonal to the filter axial direction X of 15 mm in length × 15 mm in width and a length of 20 mm in the filter axial direction X. Next, the test piece is housed in the measurement cell of the mercury porosimeter, and the pressure inside the measurement cell is reduced. After that, mercury is introduced into the measurement cell and pressurized, and the pore diameter and the pore volume are measured from the pressure at the time of pressurization and the volume of mercury introduced into the pores 110 of the partition wall 11 in the test piece. The measurement is performed in the pressure range of 0.5 to 20000 psia. In addition, 0.5 psia ^{corresponds to 0.35 × 10 -3} kg / mm ² , and 20000 psia corresponds to 14 kg / mm ² . The range of the pore diameter corresponding to this pressure range is 0.01 to 420 μm. As a constant when calculating the pore diameter from the pressure, a contact angle of 140 ° and a surface tension of 480 dyn / cm are used. The average pore diameter A is a pore diameter (pore diameter at an integrated value of 50% of the pore volume) d ₅₀ at which the cumulative pore volume is 50% in the pore diameter distribution of the partition wall 11.

In the exhaust gas purification filter 1, the average surface opening diameter of the pores 110 on the surface of the partition wall 11 is set to B μm. In the exhaust gas purification filter 1, the ratio calculated by the formula of 100 × (AB) / B represented by the above-mentioned average pore diameter A and average surface opening diameter B is 30% or less. The average surface opening diameter B of the pores 110 on the surface of the partition wall 11 is measured as follows.

A surface opening 113 is formed by pores 110 on the surface of the partition wall 11 on the side where the exhaust gas G flows in and the surface of the partition wall 11 on the side where the exhaust gas G flows out. Here, a scanning electron microscope (SEM) is used to acquire a backscattered electron image of the partition wall 11 surface on the side where the exhaust gas G flows in (that is, the partition wall 11 surface facing the first cell 121 described above). However, the surface of the partition wall 11 in the portion where the sealing portion 13 is present is excluded. At this time, the acceleration voltage can be 10 kV and the magnification can be 300 times. FIG. 4 shows an example of a backscattered electron image on the surface of the partition wall 11. In the backscattered electron image of FIG. 4, the black region is the surface opening 113 on the surface of the partition wall 11, and the light gray region is the skeleton portion 114 on the surface of the partition wall 11. Next, using image analysis software (WinROOF, manufactured by Mitani Corporation), the captured image is binarized. The binarization treatment aims to distinguish between the surface opening 113 on the surface of the partition wall 11 and the skeleton portion 114 on the surface of the partition wall 11. Since the surface opening 113 and the skeleton portion 114 have different brightnesses from each other, in the binarization process, noise remaining in the captured image is removed, an arbitrary threshold value is set, and then the binarization process is performed. Since the threshold value differs depending on the captured image, a threshold value capable of separating the surface opening 113 and the skeleton portion 114 is set for each captured image while visually checking the captured image. FIG. 5 shows an example of a binarized image. In the binarized image of FIG. 5, the light gray region is the surface opening 113 on the surface of the partition wall 11, and the black region is the skeleton portion 114 on the surface of the partition wall 11. For the surface opening 113 in the obtained binarized image, the equivalent circle diameter, which is the diameter of a perfect circle having the same area as the area of the surface opening 113, is calculated for each surface opening 113, and all the calculated circles are equivalent. The value obtained by integrating the diameters and dividing by the number of surface openings 113 is taken as the surface opening diameter. The average value of each surface opening diameter obtained from each binarized image obtained for any five different locations on the partition wall 11 surface as described above is defined as the average surface opening diameter B of the pores 110 on the partition wall 11 surface. ..

In the exhaust gas purification filter 1, the value of the average pore diameter A of the partition wall 11 defined as described above is equal to or larger than the average surface opening diameter B of the pores 110 on the surface of the partition wall 11 (A ≧ B). Further, the exhaust gas purification filter 1 is represented by 100 × (A−) represented by the value of the average pore diameter A of the partition wall 11, the average pore diameter A of the partition wall 11, and the average surface opening diameter B of the pores 110 on the surface of the partition wall 11. The ratios calculated by the formulas B) / B are each within the specific range described above. As a result, the exhaust gas purification filter 1 can secure the initial PM collection rate, reduce the initial pressure loss, and suppress the increase in pressure loss after ash accumulation. Hereinafter, the mechanism for obtaining such an effect will be described with reference to FIGS. 6 to 12.

As shown in FIG. 6, PM2 contains solid carbon (suit) 21 as a main component, as well as soluble organic component (SOF) 22 and ash 23 derived from engine oil. As shown in FIG. 7, PM2 is collected as it passes through the pores 110 in the partition wall 11. The arrow in FIG. 7 indicates the flow of the exhaust gas G flowing in the pore 110. When the average pore diameter of the partition wall 11 is A μm and the average surface opening diameter of the partition wall 11 surface is B μm, A ≧ B is satisfied, and the value of A and the formula of 100 × (AB) / B are calculated. When PM2 containing ash 23 is collected in the partition wall 11 whose ratio is set to the above-mentioned specific range, the PM2 is collected on the surface of the partition wall 11 on the side where the exhaust gas G flows in, as shown in FIG. Segregation occurs in the vicinity of the formed surface opening 113. Further, as shown in FIG. 9, after the PM2 is regenerated, the ash content 23 contained in the PM2 remains. As shown in FIG. 10, when PM2 containing ash 23 is collected again in the partition wall 11 in a state where there is residual ash 23, PM2 segregates in the vicinity of the surface opening 113 on the surface of the partition wall 11 and the residual ash content. It also accumulates near 23. As shown in FIG. 11, the surface opening 113 on the surface of the partition wall 11 is crosslinked by the ash 23 by repeating the deposition of PM2 containing the ash 23 and the regeneration process of PM2. After that, as illustrated in FIG. 12, the ash 23 that had crosslinked the surface opening 113 was peeled off during the regeneration of PM2 or the flow of the exhaust gas G, and the peeled ash 23 was the sealing portion 13 on the gas outflow side. Will be transported to. The transported ash 23 is deposited on the most downstream portion 10 of the filter (see FIG. 3, which can also be referred to as a filter bottom portion). The ash 23 covering the outer surface of the partition wall 11 increases the pressure loss, but the ash 23 deposited on the most downstream portion 10 of the filter does not easily increase the pressure loss. That is, when the average pore diameter of the partition wall 11 is A μm and the average surface opening diameter of the surface of the partition wall 11 is B μm, A ≧ B is satisfied, and the value of A and the formula of 100 × (AB) / B are used. By adopting the partition wall 11 in which the calculated ratio is within the above-mentioned specific range, the ash content 23 is crosslinked at the surface opening 113 of the partition wall 11, and the above-mentioned ash content 23 is likely to be peeled off. As a result, it becomes possible to increase the amount of ash 23 deposited on the filter most downstream portion 10 as compared with the ash 23 covering the outer surface of the partition wall 11. If the amount of ash 23 deposited on the most downstream portion 10 of the filter increases, the gas permeability of the partition wall 11 after the accumulation of ash 23 also increases, resulting in low pressure loss. It is considered that the above mechanism makes it possible not only to secure the initial PM collection rate of the exhaust gas purification filter 1 and to reduce the initial pressure drop, but also to suppress the increase in the pressure drop after the ash 23 is deposited.

In the exhaust gas purification filter 1, when the average pore diameter A is smaller than the average surface opening diameter B (A <B), PM2 containing the ash 23 easily penetrates into the pores 110 of the partition wall 11, and the ash 23 easily enters the pores 110. It becomes easy to deposit in. Therefore, it becomes difficult for the ash 23 bridged to the surface opening 113 to peel off, and it becomes difficult to suppress the increase in pressure loss due to the accumulated residual ash 23 during the aged use of the vehicle.

In the exhaust gas purification filter 1, when the average pore diameter A of the partition wall 11 is less than 5 μm, the initial pressure drop reduction effect is diminished, and the pressure loss after the ash 23 is deposited tends to increase. On the other hand, when the average pore diameter A of the partition wall 11 is 15 μm or more, the initial PM collection performance is deteriorated, and the pressure loss after the ash 23 is deposited tends to increase.

In the exhaust gas purification filter 1, when the ratio calculated by the formula of 100 × (AB) / B exceeds 30%, the difference between the average pore diameter A and the average surface opening diameter B becomes large, and the ash content 23 is increased. The PM2 contained therein is likely to be deposited inside the partition wall 11, and the ash 23 is difficult to be peeled off, resulting in an increase in pressure loss due to the residual accumulated ash 23 in the aged use of the vehicle. Since the exhaust gas purification filter 1 satisfies A ≧ B as described above, the surface opening diameter of the pores 110 on the surface of the partition wall 11 is smaller than the pore diameter inside the partition wall 11 and is 100 × ( The ratio calculated by the formula AB) / B is 0% or more.

In the exhaust gas purification filter 1, the surface opening ratio of the pores 110 on the surface of the partition wall 11 on the side where the exhaust gas G flows can be 25% or more and 40% or less. By setting the surface opening ratio of the pores 110 on the surface of the partition wall 11 to 25% or more, the number of surface openings that are the inlets of the exhaust gas G into the partition wall 11 increases, and the flow velocity of the exhaust gas G slows down, so that the initial pressure loss is reduced. It becomes easier to obtain the effect. Further, by setting the surface opening ratio of the pores 110 on the surface of the partition wall 11 to 40% or less, PM2 containing the ash content 23 is less likely to be deposited inside the partition wall 11, and it is easy to suppress an increase in pressure loss after the ash content 23 is deposited.

The surface aperture ratio of the pores 110 on the surface of the partition wall 11 is an expression of 100 × (total value of the area of each surface opening 113 in all the above-mentioned binarized images) / (total value of the area of all the binarized images). Can be calculated from. All binarized images mean the above-mentioned five binarized images.

In the exhaust gas purification filter 1, the porosity of the partition wall 11 can be 50% or more and 70% or less. By setting the porosity of the partition wall 11 to 50% or more, it becomes easy to secure a flow path through which the exhaust gas G passes through the partition wall 11, so that it becomes easy to reduce the initial pressure loss. Further, by setting the porosity of the partition wall 11 to 70% or less, it becomes easy to secure the strength of the exhaust gas purification filter 1 itself, and it becomes easy to suppress cracks due to stress at the casing and heat generation during the regeneration process of PM2. The porosity of the partition wall 11 can be preferably 52% or more, more preferably 60% or more, from the viewpoint of reducing initial pressure loss and the like. Further, the porosity of the partition wall 11 can be preferably 68% or less, more preferably 67% or less, still more preferably 66% or less, from the viewpoint of improving the strength of the exhaust gas purification filter 1. The upper and lower limits can be arbitrarily combined.

The porosity of the partition wall 11 is measured by a mercury porosimeter using the principle of the mercury intrusion method described above. Specifically, the porosity of the partition wall 11 can be calculated from the following relational expression.
Porosity (%) of partition wall 11 = total pore volume / (total pore volume + 1 / true specific gravity of partition wall material) × 100
When the partition wall material is cordierite, 2.52 can be used as the true specific density of cordierite.

_{In the exhaust gas purification filter 1, the pore diameter (pore diameter at an integrated value of 75% of the pore volume) d 75} in which the cumulative pore volume in the pore diameter distribution of the partition wall 11 by the mercury porosimeter using the principle of the mercury injection method described above is 75%. The exhaust gas purification filter 1 shall be configured to satisfy XY ≦ 7 μm, where X μm and the pore diameter (pore diameter at the integrated value of 25% of the pore volume) d _{25 where the cumulative pore volume is 25% are Y μm.} Can be done. According to this configuration, the flow velocity of the exhaust gas G tends to be uniform, and it is possible to reliably suppress the increase in pressure loss after ash accumulation.

The XY can be preferably 6.8 μm or less, more preferably 6.5 μm or less, from the viewpoint of suppressing an increase in pressure loss after ash accumulation. From the viewpoint of cost and the like, XY can be preferably 3.5 μm or more, more preferably 5.0 μm or more.

The exhaust gas purification filter 1 sets the gas permeability coefficient of the partition wall 11 at _{the position X 10} (see FIG. 2) 10 mm from the filter end face 15 on the exhaust gas inflow side in a state where the ash 23 of 20 g / L or more and 40 g / L or less is deposited. _10, when the gas permeability coefficient of the partition wall at the center position X _{C (see} FIG. 2) between the filter end face 16 of the filter end face 15 and the exhaust gas outflow side of the exhaust gas inlet side was set to k _c, the gas permeability coefficient ratio k _c / the value of k ₁₀ is Ru der 1.5 or less. According to this configuration, it is possible to ensure the suppression of the increase in pressure loss after the accumulation of ash.

In the above, when the accumulated amount of the ash 23 is less than 20 g / L, the position X ₁₀ from the filter end face 15 on the exhaust gas inflow side to 10 mm, and between the filter end face 15 on the exhaust gas inflow side and the filter end face 16 on the exhaust gas outflow side. Since the ash 23 is not deposited on the outside of the partition wall 11 or is in a trace amount in both the central positions X and _{C, it is difficult to understand the effect of the peeling of the ash 23.} Therefore, in the above, the accumulated amount of ash 23 is set to 20 g / L or more. On the other hand, when the accumulated amount of the ash 23 is more than 40 g / L, the ash 23 that has peeled off and accumulated on the most downstream portion 10 of the filter increases, and is between the filter end surface 15 on the exhaust gas inflow side and the filter end surface 16 on the exhaust gas outflow side. It believed that extends its influence to the central position X _C, difficult to understand the effects due to separation of the ash 23. Therefore, in the above, the accumulated amount of ash 23 is 40 g / L or less.

k _c / k ₁₀ is an index showing the magnitude relationship between the gas permeability coefficient k _c and the gas permeability coefficient k _10. The gas permeability coefficient of the partition wall 11 becomes smaller as the ash content 23 is deposited. Further, the flow velocity of the exhaust gas G introduced into the cell 12 of the exhaust gas purification filter 1 is such that the position X10 ₁₀ mm from the filter end surface 15 on the exhaust gas inflow side is the filter end surface 15 on the exhaust gas inflow side and the filter on the exhaust gas outflow side. faster than the center position X _C between the end face 16. That is, towards the position X ₁₀ of 10mm from the filter end face 15 of the exhaust gas inlet side, the deposition amount of ash 23 than the center position X _C between the filter end face 16 of the filter end face 15 and the exhaust gas outflow side of the exhaust gas inlet side There are many relationships. When this is replaced with the gas permeability coefficient, _{the relationship between the gas permeability coefficient k 10} and the gas permeability coefficient k _c after the ash 23 is deposited is larger in the gas permeability coefficient k _c than in the gas permeability coefficient k _10. That is, in the conventional exhaust gas purification filter not provided with the configuration of the present disclosure, _{the value of k c} / k ₁₀ is usually large. As will be described later in an experimental example, specifically, when _{the value of k c} / k ₁₀ exceeds 1.5, the rate of increase in pressure drop after the accumulation of ash 23 with respect to the initial pressure drop becomes high, which is not preferable. It is considered that this is because the ash content 23 on the surface of the partition wall 11 at _{the position X10 10} mm from the filter end surface 15 on the exhaust gas inflow side is not peeled off and is deposited in the pores 110. Therefore, in order to suppress the pressure drop increase rate, _{the value of k c} / k ₁₀ is preferably 1.5 or less. It is considered that this is because the peeling of the ash 23 on the surface of the partition wall 11 is promoted around _{the position X 10} 10 mm from the filter end surface 15 on the exhaust gas inflow side. However, not all the ash 23 is peeled off, transported to the vicinity of the sealing portion 13 of the most downstream portion 10 of the filter, and deposited. A part of the ash 23 remains in the partition wall 11 and near the surface of the partition wall 11. As a result of the above, in _{the range where the value of k c} / k ₁₀ is 1.5 or less, it is possible to keep the rate of increase in pressure drop after the accumulation of ash 23 with respect to the initial pressure drop low.

The gas permeability coefficients k ₁₀ and k _c are measured as follows. First, an ash content 23 of 20 g / L or more and 40 g / L or less is deposited on the exhaust gas purification filter 1. The accumulation of the ash content 23 can be carried out by operating the gasoline engine using gasoline containing 2% of the ash content derived from the engine oil and depositing the ash content on the exhaust gas purification filter 1 mounted on the exhaust passage. Specifically, (1) PM2 is deposited under the condition of (1) a stoichiometric atmosphere and the center temperature of the exhaust gas purification filter 1 at 800 ° C. for 9 minutes, and (2) under the atmosphere atmosphere and the center temperature of the exhaust gas purification filter 1 is 800 ° C. PM2 is regenerated at ~ 900 ° C. for 1 minute. By repeating the deposition of PM2 according to (1) above and the regeneration treatment of PM2 according to (2) above, the ash 23 is deposited on the exhaust gas purification filter 1. The accumulated amount of the ash content 23 can be grasped by appropriately taking out the exhaust gas purification filter 1 and measuring the weight.

Next, regarding the exhaust gas purification filter 1 in which the predetermined amount of ash 23 is deposited, the position X ₁₀ 10 mm from the filter end face 15 on the exhaust gas inflow side, the filter end face 15 on the exhaust gas inflow side, and the filter end face 16 on the exhaust gas outflow side. from the center position X _C between, for hollowing respectively taken measurement sample without a seal 13. At this time, _{the measurement sample at the position X 10} is collected so that the position 10 mm from the filter end face 15 on the exhaust gas inflow side is the upstream end face. On the other hand, the measurement sample in the central position X _C are collected so that the central position X _C is the upstream end face. The shape of each measurement sample is a cylindrical shape having a diameter of 30 mm and a length of 25 mm in the filter axial direction. The skin portion 14 of each hollowed out measurement sample can be formed by, for example, cementing.

Next, as illustrated in FIG. 13, polyester tapes 315a and 316a are attached to both end faces 315 and 316 of the measurement sample 3 in the filter axial direction X, respectively. Next, the polyester tapes 315a and 316a are partially disappeared by, for example, a soldering iron so that the alternating sealing portions 13 are formed by the polyester tapes 315a and 316a. In this way, in the upstream end surface 315, which is the filter end surface on the exhaust gas inflow side in the measurement sample 3, for example, 13 cells 12 are opened and the remaining cells 12 are opened as illustrated in FIG. 14 (a). It is closed by the sealing portion 13 made of polyester tape 315a. On the other hand, in the downstream end surface 316, which is the filter end surface on the exhaust gas outflow side in the measurement sample 3, for example, 24 cells 12 are opened and the remaining cells 12 are made of polyester tape 316a, as illustrated in FIG. 14 (b). It is closed by the sealing portion 13 made of. That is, instead of the sealing portion 13 made of ceramics, the sealing portion 13 made of polyester tapes 315a and 316a is formed. Here, in measuring the gas permeability coefficient, the measurement sample 3 in which the sealing portion 13 is formed by the polyester tapes 315a and 316a has been described, but the measurement sample 3 in which the sealing portion 13 made of ceramics is formed may also be used. Similar results are obtained.

Next, as illustrated in FIG. 13, gas is flowed from the upstream end surface 315 of the measurement sample 3 toward the downstream end surface 316 of the measurement sample 3, and the relationship between the gas flow velocity and the pressure loss is measured by the palm pollometer 4. do. Specifically, the pressure loss when the gas flow velocity is changed is measured. The arrow in FIG. 13 indicates the gas flow. Then, the relationship diagram between the gas flow velocity (X-axis) and the pressure loss (Y-axis) is obtained. FIG. 15 shows an example of a relationship diagram between the gas flow velocity (X-axis) and the pressure loss (Y-axis). In this relationship diagram, the measured value (plot point) by the palm pollometer 4 and the calculated value (broken line) obtained by the following equations (i) to (viii) are shown. Hereinafter, equations (i) to (viii) will be described.

The sum of the pressure loss ΔP (unit: Pa) of the exhaust gas purification filter 1, the condensed pressure loss ΔP _inlet when the gas flows into the cell 12, and the expanded pressure drop ΔP _{exit when the gas flows out from the cell 12 ΔP inlet / exit} (unit: unit). _{: Pa), the pressure drop ΔP channel} (unit: Pa) in the gas passage in the cell 12, _{and the pressure drop ΔP wall} (unit: Pa) in the gas passage of the partition wall 11 satisfy the relationship of the following formula (i).
ΔP = ΔP _{inlet / exit} + ΔP _channel + ΔP _wall ... (i)

Further, ΔP _{inlet / exit} , the opening area A _open (unit: m ² _{) of the cell 12, the opening area A in} (unit: m ² ) of the cell 12 at the filter end face 15 on the exhaust gas inflow side, and the gas flow velocity in the cell 12. The V _channel (unit: m / s) and the air density ρ (unit: kg / m ³ ) satisfy the relationship of the following equation (ii).

Further, the ΔP _channel + ΔP _wall , the gas permeation coefficient k (unit: m ² ), the length L (unit: m) of the filter axial direction X of the exhaust gas purification filter 1, and the hydraulic diameter a ₁ (unit: m) of the cell 12. m), the thickness w of the partition wall 11 (unit: m), the friction coefficient F in the cell 12 (unit: dimensionless), the Reynolds number (unit: dimensionless), and the gas viscosity μ (unit: Pa · s). ) And the gas flow velocity V _channel (unit: m / s) in the cell 12 satisfy the relationship of the following equations (iii) to (viii). In equation (iii), e is an exponential function exp.

The pressure drop value is calculated based on the above equations (i) to (viii). The broken line based on the calculated value shown in the relationship diagram between the gas flow velocity (X-axis) and the pressure loss (Y-axis) illustrated in FIG. 15 is the pressure drop value obtained by calculation. As can be understood from the equations (i) to (viii), the pressure drop value _{measures the filter length L, the cell opening area A open} , the hydraulic diameter a ₁ , and the thickness w of the partition wall 11, excluding the gas permeability coefficient k. These values do not change even if the gas flow velocity is changed. Therefore, by inputting an arbitrary value to the gas permeability coefficient, the calculated value in the relationship diagram between the gas flow velocity (X-axis) and the pressure loss (Y-axis) can be derived.

For example, if a value having a large gas permeability coefficient is input, the pressure loss value becomes lower than the actually measured value, and the calculated value is lower than the actually measured value. On the other hand, if a value with a small gas permeability coefficient is input, the calculated value exceeds the measured value. Therefore, in order to approximate the calculated value so as to be closest to the measured value, the gas permeability coefficient k that minimizes the difference between the calculated value and the measured value is calculated by the least squares method. This calculated value is the gas permeability coefficient k. That is, the gas permeability coefficient k is a value obtained by back-calculating the gas permeability coefficient from the measured values of the pressure loss measured by the palm polo meter from the equations (i) to (viii). _{As described above, the gas permeability coefficients k 10} and k _c at a predetermined position in a state where a predetermined amount of ash is deposited can be obtained.

The exhaust gas purification filter 1 described above can exert a sufficient effect when used in a state where the catalyst is not supported on the partition wall 11.

<Experimental example>
Each exhaust gas purification filter of the Example and the comparative example will be described. In this experimental example, the exhaust gas purifying _{filter, SiO} 2: 45 wt% to 55 wt% or _less, Al ₂ O 3: 33 wt% to 42 wt% or less, MgO: chemical containing 12 wt% to 18 wt% or less The main component is cordierite having a composition. The fact that cordierite is the main component means that 50% by mass or more of cordierite is cordierite. Therefore, in producing each exhaust gas purification filter in this experimental example, a cordierite forming raw material containing a Si source, an Al source, and an Mg source is used so that cordierite is produced by firing.

-Manufacturing of exhaust gas purification filter-
(Example 1)
In producing the exhaust gas purification filter of Example 1, porous silica (Si source), talc (Mg source), and aluminum hydroxide (Al source) are blended so as to have the blending ratio (mass%) shown in Table 1. As a result, a raw material for forming cordierite was prepared.

The bulk density of the porous silica used is 0.18 g / cm ³ . For the measurement of bulk density, a tap densor manufactured by Seishin Enterprise Co., Ltd., which is a tap density method fluidity adhesive force measuring instrument, was used. Specifically, after the cylinder of the measuring instrument was filled with silica, the silica was compressed by tapping, and the bulk density was calculated from the mass of the compressed silica and the volume of the cylinder. Further, as the aluminum hydroxide, one having an average particle diameter of 3 μm and one having an average particle diameter of 8 μm were used. The "average particle size" refers to the particle size when the volume integrated value in the particle size distribution obtained by the laser diffraction / scattering method is 50%.

Water (solvent), methyl cellulose (binder), and a dispersant are added to the cordierite forming raw material so as to have the blending ratio (mass%) shown in Table 1, and the cordierite forming raw material is mixed by a kneader. A cordierite containing the above was prepared. The dispersant mainly suppresses aggregation of particles and improves solubilization property. Specifically, polyoxyethylene polyoxypropylene glyceryl ether having an average molecular weight of 4550 was used.

Here, in the raw material system using porous silica as in Example 1, since there are many gaps between the particles, a large amount of solvent (here, water) is required for soil formation. In order to improve the above-mentioned solvability in such a large amount of solvent, it is effective to strengthen the kneading at the time of kneading the clay. However, it is difficult to suppress the aggregation of particles by the kneading and directly confirm whether or not the particles are dispersed in the clay.

Therefore, in this experimental example, the soil density deviation rate was introduced as a new index of particle dispersibility in the kneaded soil. Specifically, the clay before extrusion molding is taken out with a mold, and the clay at eight places is randomly taken out. The extracted soil is put into a measuring instrument with a diameter of 25 mm and a length of 20 mm in the pressure measuring instrument "Autograph" manufactured by Shimadzu Corporation, and the volume of the soil taken out by compressing with a pressure of 1 kN and the volume of the soil and the volume of the extracted soil. Calculate the soil density from the weight. The average value of the soil densities calculated for the eight soils is taken as the measured soil density. On the other hand, the soil density calculated in advance from the mixing ratio of the raw materials is used as the calculated soil density. It is possible to judge the particle dispersibility by confirming the difference (deviation rate) of the soil density by the actual measurement with respect to the soil density by this calculation. As the measured soil density becomes smaller than the calculated soil density, the wettability of the dispersant is poor and more air is present on the particle surface, resulting in poor particle dispersibility. On the other hand, the closer the measured soil density is to the calculated soil density value, the better the particle dispersibility.

In Example 1, the speed of the kneader and the number of times the soil was repeatedly passed through the kneader were arbitrarily changed, and the following soil density deviation rate was adjusted to be less than 10%. In addition, when the speed of the kneader is increased, the soil density deviation rate tends to decrease. In addition, as the number of times the soil is repeatedly passed through the kneader, the soil density deviation rate tends to decrease.
Soil density deviation rate (%) = 100 × {(calculated soil density)-(measured soil density)} / (calculated soil density)

The clay prepared as described above was formed into a honeycomb shape by extrusion molding. The molded product was cut to a predetermined length after drying.

Next, the molded product was fired at 1430 ° C. to obtain a sintered body having a honeycomb structure.

Next, using the dipping method, the exhaust gas inflow end face and the exhaust gas outflow end face of the cell were alternately filled and fired with a slurry containing a ceramic raw material of the same type as the sintered body having a honeycomb structure to form a sealed portion.

As described above, the exhaust gas purification filter of Example 1 was produced.

(Examples 2 to 8)
In Example 1, the average particle size and bulk density of the porous silica in the cordierite forming raw material were changed. The larger the average particle size of the porous silica, the larger the pore diameter of the formed partition wall, and the smaller the bulk density of the porous silica, the higher the porosity of the formed partition wall. Further, when the ratio of the particle size is increased in the compounding of aluminum hydroxide having different particle sizes, the surface aperture ratio and the average surface opening diameter become large. Further, by increasing the heating rate between 1200 ° C. and 1430 ° C. during firing, the pore diameter and the average surface opening diameter can be increased. It was produced by combining these conditions. The total blending ratio of aluminum hydroxide was the same as that of Example 1, the blending of aluminum hydroxide having different particle sizes was changed, and the blending ratio of other clay was the same as that of Example 1. Then, in the same manner as in Example 1, the speed of the kneader and the number of times the soil is repeatedly passed through the kneader are arbitrarily changed, and the soil density deviation rate is adjusted to be less than 10%. By changing the heating rate between 1200 ° C. and 1430 ° C. during firing, the exhaust gas purification filters of Examples 2 to 8 were produced.

(Example 9)
In Example 1, the average particle size and bulk density of the porous silica in the cordierite forming raw material are changed, and the speed of the kneader and the number of times the clay is repeatedly passed through the kneader are arbitrarily changed to dissociate the clay density. The exhaust gas purification filter of Example 9 was produced by using silica soil adjusted so that the rate was 10% or more. The bulk density of the porous silica used is 0.25 g / cm ³ .

(Example 10, Example 11)
In Example 9, the average particle size and bulk density of the porous silica in the cordierite forming raw material were changed. Other than that, the exhaust gas purification filters of Examples 10 and 11 were produced by adjusting the soil so that the soil density deviation rate was 10% or more in the same manner as in Example 9.

(Comparative Example 1)
In producing the exhaust gas purification filter of Comparative Example 1, fused silica (Si source), talc (Mg source), and aluminum hydroxide (Al source) are blended so as to have the blending ratio (mass%) shown in Table 2. Prepared a raw material for forming cordierite. The bulk density of the molten silica used is 1.30 g / cm ³ .

Water (solvent), methyl cellulose (binder), lubricating oil, and graphite are added to the cordierite forming raw material so as to have the blending ratio shown in Table 2, and the cordierite forming raw material is contained by mixing with a kneader. I made graphite. Lubricating oil is intended to improve the slippage of the clay, the molding machine and the metal part of the mold surface to increase the molding speed. As the lubricating oil, rapeseed oil, which is a vegetable oil, was used. In addition, the soil density deviation rate was adjusted to be less than 10% by arbitrarily changing the speed of the kneader and the number of times the soil was repeatedly passed through the kneader. Using the clay prepared as described above, the exhaust gas purification filter of Comparative Example 1 was produced in the same manner as in Example 1 thereafter.

(Comparative Example 2, Comparative Example 3)
In Comparative Example 1, the average particle size of molten silica and talc and the blending ratio of graphite in the cordierite forming raw material were changed. Other than that, the exhaust gas purification filters of Comparative Example 2 and Comparative Example 3 were produced by adjusting the soil so that the soil density deviation rate was less than 10% in the same manner as in Comparative Example 1.

(Comparative Example 4)
In producing the exhaust gas purification filter of Comparative Example 4, porous silica (Si source), talc (Mg source), and aluminum hydroxide (Al source) are blended so as to have the blending ratio (mass%) shown in Table 3. As a result, a raw material for forming cordierite was prepared. The bulk density of the porous silica used is 0.25 g / cm ³ .

Water (solvent), methylcellulose (binder), and lubricating oil are added to the cordierite-forming raw material so as to have the blending ratios shown in Table 3, and the clay is mixed with a kneader to contain the cordierite-forming raw material. Was produced. As the lubricating oil, rapeseed oil, which is the same vegetable oil as above, was used. In addition, the soil density deviation rate was adjusted to be 10% or more by arbitrarily changing the speed of the kneader and the number of times the soil was repeatedly passed through the kneader. Using the clay prepared as described above, the exhaust gas purification filter of Comparative Example 4 was produced in the same manner as in Example 1 thereafter.

(Comparative Example 5, Comparative Example 6)
In Comparative Example 4, the average particle size and bulk density of the porous silica in the cordierite forming raw material were changed. Other than that, the exhaust gas purification filters of Comparative Example 5 and Comparative Example 6 were produced by adjusting the soil so that the soil density deviation rate was 10% or more in the same manner as in Comparative Example 4.

-Measurement of partition wall characteristics-
The partition wall characteristics of the exhaust gas purification filters of Examples and Comparative Examples were measured. Specifically, according to the above-mentioned measurement method, the average pore diameter A of the partition wall, XY (pore diameter d ₇₅ -pore diameter d ₂₅ ) in the pore diameter distribution of the partition wall, and the porosity of the partition wall were measured. At this time, Autopore IV9500 manufactured by Shimadzu Corporation was used as the mercury porosimeter. Further, according to the above-mentioned measurement method, the average surface opening diameter B of the pores on the partition wall surface and the surface opening ratio of the pores on the partition wall surface were measured. At this time, Quanta250FEG manufactured by FEI was used as the SEM. The image analysis software includes WinROOF Ver. 7.4 was used. Further, the ratio calculated by the formula of 100 × (AB) / B was calculated from the average pore diameter A of the obtained partition wall and the average surface opening diameter B of the pores on the partition wall surface. Further, the value of _{the gas permeability coefficient ratio k c} / k ₁₀ was measured according to the above-mentioned measuring method. At this time, CEP-1100AXSHJ manufactured by Porous Materials was used as the palm pollometer.

-Evaluation-
For each exhaust gas purification filter, the initial PM collection rate, initial pressure drop, and pressure drop after ash accumulation were measured. The initial PM collection rate, initial pressure loss, and pressure loss after ash accumulation are φ118.4 mm (filter diameter) x L120 mm (filter length), the bulkhead thickness is 8.5 mil, and the number of cells is 300 cpsi. An exhaust gas purification filter having a certain cell structure was used.

(Initial PM collection rate, initial pressure drop)
The initial PM collection rate was measured as follows. The produced exhaust gas purification filter was installed in the exhaust pipe of a gasoline direct injection engine, and the exhaust gas containing PM was flowed through the exhaust gas purification filter. _{At this time, N in} , which is the number of PMs in the exhaust gas before flowing into the exhaust gas purification filter, and _{N out} , which is the number of PMs in the exhaust gas flowing out from the exhaust gas purification filter, are measured and 100 × (N _{in −} N _out ) /. The initial PM collection rate was calculated from the _{N in formula.} At this time, the measurement conditions were a temperature of 450 ° C. and an exhaust gas flow rate of 2.8 m ³ / min. For the measurement of the PM number, a PM particle number counter "AVL-489" manufactured by AVL was used. On the other hand, the initial pressure drop was measured as follows. At the same time as the measurement of the initial PM collection rate, the pressure before the exhaust gas purification filter (upstream) and the pressure after the exhaust gas purification filter (downstream) were measured by the pressure sensor, and the difference was taken as the initial pressure drop. At this time, the measurement conditions were a temperature of 720 ° C. and an exhaust gas flow rate of 11.0 m ³ / min. For each measurement, each exhaust gas purification filter in the initial state in which PM was not deposited and in which the catalyst was not coated was used.

In this experimental example, the case where the initial PM collection rate was 80% or more was designated as "A" because the initial PM collection rate was sufficiently secured. When the initial PM collection rate was 70% or more and less than 80%, it was designated as "B" as the initial PM collection rate was secured. When the initial PM collection rate was less than 70%, it was designated as "C" because the initial PM collection rate was not secured. Further, when the initial pressure drop was 6 kPa or less, it was designated as "A" because the effect of reducing the initial pressure drop was sufficiently obtained. When the initial pressure drop was more than 6 kPa and 7 kPa or less, it was designated as "B" because the effect of reducing the initial pressure drop was obtained. When the initial pressure drop was more than 8 kPa, it was designated as "C" because the effect of reducing the initial pressure drop could not be obtained.

(Pressure loss after ash accumulation)
Ash content of 20 g / L or more and 40 g / L or less was deposited on each exhaust gas purification filter in the initial state in which PM was not deposited and on which the catalyst was not coated. The accumulation of ash was carried out by operating a gasoline engine using gasoline containing 2% of ash derived from engine oil and depositing ash on an exhaust gas purification filter mounted on an exhaust passage. Specifically, (1) PM deposition in which PM is deposited under the condition of 9 minutes at the center temperature of the exhaust gas purification filter at 800 ° C. under a stoichiometric atmosphere, and (2) the center temperature of the exhaust gas purification filter under an atmosphere atmosphere. The ash was deposited on the exhaust gas purification filter by repeating the PM regeneration treatment of regenerating the PM at 800 ° C. to 900 ° C. for 1 minute. At this time, the accumulated amount of ash was grasped by appropriately taking out the exhaust gas purification filter and measuring the weight. After that, the pressure before the exhaust gas purification filter and the pressure after the exhaust gas purification filter were measured by the pressure sensor in the same manner as the above initial pressure loss, and the difference was taken as the pressure drop after ash accumulation. In this experimental example, when the pressure drop after ash accumulation when 30 g / L of ash was deposited was 11 kPa or less, the effect of suppressing the increase in pressure drop after ash accumulation was sufficiently obtained as "A". did. Similarly, when the pressure drop after ash accumulation was more than 11 kPa and 13 kPa or less, it was designated as "B" because the effect of suppressing the increase in pressure drop after ash accumulation was obtained. When the pressure drop after ash accumulation was more than 13 kPa, it was designated as "C" because the effect of suppressing the increase in pressure drop after ash accumulation could not be obtained. When the initial pressure drop is P _fresh and the pressure drop after ash accumulation is P _ash-loaded , the rate of increase in pressure drop after ash accumulation with respect to the initial pressure loss is 100 × ( _Pash-loaded −P _fresh ) / P _fresh . Asked more. FIG. 16 shows the relationship between the gas permeability coefficient ratio k _c / k ₁₀ and the pressure drop increase rate. Note that FIG. 16 shows the results of the exhaust gas purification filter of Example 4 as a representative example of each example.

The results of the above experiments are summarized in Table 4.

As shown in Table 4, when the average pore diameter of the partition wall is A μm and the average surface opening diameter of the partition wall surface is B μm, A ≧ B is satisfied, the value of A, and 100 × (AB) / B. The exhaust gas purification filters of Examples 1 to 11 in which the ratio calculated by the formula of the above is within the specific range specified in the present disclosure secures the initial PM collection rate and reduces the initial pressure loss. , And it was confirmed that the increase in pressure loss after ash accumulation can be suppressed.

With respect to these, the exhaust gas of Comparative Examples 1 to 6 in which the value of A and the ratio calculated by the formula of 100 × (AB) / B are outside the specific range specified in the present disclosure. The purification filter could not achieve either the securing of the initial PM collection rate, the reduction of the initial pressure drop, and the suppression of the increase in the pressure drop after the ash accumulation.

According to the exhaust gas purification filters of Examples 1 to 11, the ratio calculated by the formula of 100 × (AB) / B is 30% or less, and ash content is contained by setting A ≧ B. It can be seen that PM is less likely to be deposited inside the partition wall, and it becomes easier to suppress an increase in pressure loss due to the accumulated residual ash in the aged use of the vehicle. Further, comparing the exhaust gas purification filters of Examples 1 to 8 with the exhaust gas purification filters of Examples 9 to 11, by satisfying XY ≦ 7 μm, the initial PM collection rate is secured and the initial stage is achieved. It can be seen that the pressure loss reduction effect of the above can be easily obtained.

_{The exhaust gas purification filters of Examples 1 to 11 have a gas permeability coefficient ratio of k c} / k ₁₀ of 1.5 or less in a state where ash content of 20 g / L or more and 40 g / L or less is deposited. According to this configuration, as shown in FIG. 16, it can be said that the suppression of the pressure drop increase after the ash accumulation can be ensured.

The present invention is not limited to each of the above embodiments and experimental examples, and various modifications can be made without departing from the gist thereof. In addition, each configuration shown in each embodiment and each experimental example can be arbitrarily combined.

1 Exhaust gas purification filter 11 Partition wall 110 Pore 12 Cell 13 Sealed part G Exhaust gas

Claims (3)

An exhaust gas purification filter (1) placed in the exhaust passage of a gasoline engine.
A partition wall (11) having a large number of pores (110) and
A plurality of cells (12,121,122) partitioned by the partition wall, and
It has a sealing portion (13) that alternately seals a plurality of the above cells at both ends of the filter.
When the average pore diameter of the partition wall is A μm and the average surface opening diameter of the pores on the partition wall surface is B μm.
A ≧ B is satisfied, and A is 5 μm or more and less than 15 μm.
Ri der percentage 30% or less calculated by the 100 × formula (A-B) / B,
In a state where ash (23) of 20 g / L or more and 40 g / L or less is deposited,
The gas permeability coefficient of the partition wall at _{a position (X 10} ) 10 mm from the filter end face (15) on the exhaust gas inflow side _{is k 10} , and the center between the filter end face on the exhaust gas inflow side and the filter end face (16) on the exhaust gas outflow side. When the gas permeability coefficient of the partition wall at the position (X _{C ) is k c} ,
An exhaust gas purification filter (1) having a gas permeability coefficient ratio of k _c / k ₁₀ of 1.5 or less. In the pore diameter distribution of the partition wall, when the pore diameter d _{75 having a cumulative pore volume of 75% is X μm and the pore diameter d 25} having a cumulative pore volume of 25% is Y μm.
The exhaust gas purification filter according to claim 1, which satisfies XY≤7 μm. The exhaust gas purification filter according to claim 1 or 2, wherein the surface opening ratio of the pores on the partition wall surface is 25% or more and 40% or less.

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